Radiation curable polyene-polythiol coating compositions

ABSTRACT

The invention disclosed is directed to a method for overcoating which includes applying to a substrate a novel photocurable lacquer composition having as essential ingredients a polyene selected from a particular group of polyenes which contain at least 2 reactive unsaturated carbon-to-carbon bonds per molecule, a polythiol containing 2 or more thiol groups per molecule and a resin component; and thereafter exposing the applied composition to actinic radiation for a period of time sufficient to photocure the applied composition to provide an overcoating. Optionally, a sensitizer may be included if desired to decrease curing time and improve efficiency. The method is particularly useful for high speed overcoating printed metal articles such as cans. Overcoatings thus provided are found to be characterized by high strength, good scratch resistance, freedom from tackiness and excellent transparency.

[451 Dec. 17, 1974 RADIATION CURABLE POLYENE-POLYTHIOL COATINGCOMPOSITIONS Inventors: James L. Guthrie, Ashton; Francis J. Rendulic,Ellicott City, both of Md.

W. R. Grace & Co., New York, N.Y.

Filed: Aug. 16, 1973 Appl. No.: 388,860

Related U.S. Application Data Division of Ser. No. 209,369, Dec. 17,1971, Pat. No. 3,787,303.

Assignee:

U.S. Cl 204/159.15, 117/9331, 117/132 R, 117/132 B, 117/155 R, 117/155UA, 204/159.14, 204/159.18,204/159.19,

260/16, 260/31.8 M, 260/31.8 XA, 260/31.8 .z. 26.0133 R 2,6 69/7 2 01UA, 260/837 R, 260/829, 260/861, 260/865,

Int. Cl B0lj 1/10, BOlj l/l2 Field of Search..... 204/l59.l4, 159.18,159.15, 204/159.19; 260/77.5,79.7, 79.5 R, 79, 75 S UA References CitedUNITED STATES PATENTS 12/1971 Oswald et al. 204/l59.18

3,656,999 4/1972 Lundsager 260/79 3,661,744 5/1972 Nehr et al 204/l59.l43,662,023 5/1972 Nehr et al 260/79.5 C 3,787,303 1/1974 Guthrie et al204/l59.15

Primary Examiner.lohn C. Bleutge Assistant ExaminerRichard B. TurnerAttorney, Agent, or FirmCharles L. Harness 5 7 ABSTRACT The inventiondisclosed is directed to a method for overcoating which includesapplying to a substrate a novel photocurable lacquer composition havingas essential ingredients a polyene selected from a particular group ofpolyenes which contain at least 2 reactive unsaturated carbon-to-carbonbonds per molecule, a polythiol containing 2 or more thiol groups permolecule and a resin component; and thereafter exposing the appliedcomposition to actinic radiation for a period of time sufficient tophotocure the applied composition to provide an overcoating. Optionally,a sensitizer may be included if desired to decrease curing time andimprove efficiency. The method is particularly useful for high speedovercoating printed metal articles such as cans. Overcoatings thusprovided are found to be characterized by high strength, good scratchresistance, freedom from tackiness and excellent transparency.

8 Claims, No Drawings RADIATION. CURABLE POLYENE-POLYTHIOL COATINGCOMPOSITIONS This is a division, of application Ser. No. 209,369 filedDec. 17, 1971 now US. Pat. No. 3,787,303, issued Jan. 22, 1974.

The present invention relates to a photocurable lacquer compositionwhich includes a polyene component containing at least two unsaturatedcarbon-to-carbon bonds per molecule, a polythiol component containing onthe average at least two SH functional groups per molecule, and a resincomponent. The invention also provides a method for overcoating articleswherein an applied coating of the composition is cured by means ofactinic radiation to produce a protective coating which is typicallyclear, tough and durable.

It is well known in the art that protective functional overlayers oftransparent synthetic organic coating materials may be formed on varioussubstrates. Typically, the prior art coating materials have been bakedat high temperatures to form coatings on substrates, printed andnon-printed. Many prior art coating materials contain various harmfulsolvents which are released as vapors upon baking. Not only do thereleased vapors present pollution problems, but also baking is costlyand time consuming. Further, use of high bake temperatures often resultsin discoloration of inks or pigments disposed on the articles beingcoated. Generally, use of lower bake temperatures further slows theprior art lacquering processes, while use of higher temperatures furtherlimits the types of inks which may be satisfactorily applied prior toapplying protective overcoatings. In preparing printed cartons fromprinted paperboard, it is conventional to apply overcoatings such asheatcurable lacquers and press varnishes which, in practice, generallyhave required in process dusting with starch powders or the like andextended aging prior to making cartons from the overcoated sheets.

It has now been found by practice of the present invention that printedarticles may be overlayered with a transparent protective coating inrapid, simple and efficient manner without requiring high temperaturesor evolution of solvent vapor. Numerousdefects of prior art overcoatingcompositions and methods may be effectively overcome by the presentinvention which provides a clear coating composition and method forovercoating using actinic radiation to cure an applied coating of thecomposition. Upon exposure to actinic radiation, the composition curesrapidly to a typically clear coating which has good lubricity,withstands abrasion, exhibits high gloss, effectively adheres to avariety of substrates, and is substantially odorless. The present methodis especially useful for high-speed coating on metal substrates such asmetal sheets, printed and nonprinted, from which articles such as cansare formed. Upon curing, the composition effectively adheres to both themetal and to intermediate layers such as inks and the like whichtypically are disposed on the metal in the metal decorating field. Otherprinted substrates which may be coated using the present method includemagazine-quality paper and paper-board. Typically, printed paperboardmay be coated using the present method and thereafter passed to cartonfinishing operations without requiring aging and without need fordusting.

Generally stated, the present invention provides a method forovercoating which includes applying to a substrate a photocurablelacquer composition having (a) a polythiol component containing at leasttwo SH groups per molecule, (b) a polyene component selected fromparticular polyenes (subsequently set forth herein) which contain 2 ormore terminally positioned unsaturated carbon-to-carbon bonds permolecule and are characterized in that they will react with thepolythiol to form tough and durable coatings, and (c) a resin component.Optionally, a sensitizer component may be included if desired todecrease curing time and improve efficiency. Curing of the appliedcomposition is effected by exposure to a free radical generator such asactinic radiation to form, typically, clear, tough, durablepolythioether coatings.

Polyenes useful herein include triallyl isocyanurate; Bisphenol Adiallyl ether; the diadduct of diallyl amine and Bisphenol A4,4'-diglycidyl ether; the diadduct of a member selected from the groupconsisting of allyl alcohol, diallyl malate, and trimethylolpropanediallyl ether and a member selected from the group consisting of toluenediisocyanate 3 ,3 '-dim ethyl-4 ,4 biphenylene diisocyanate,3-isocyanatomethyl-3,5,5- trimethylcyclohexyl isocyanate 4,4methylenebis(cyclohexyl isocyanate), and Solithane 291 (trademark for apolyester isocyanate product by Thiokol having molecular weight of about2800 and prepared by reacting ethylene glycol, propylene glycol, adipicacid and toluene diisocyanate). The various polyenes may be obtainedcommercially or may be readily prepared from commercially availablereactants. Methods for preparing a number of these polyenes are setforth subsequently in the examples included in this description.Preferred polyenes are triallyl isocyanurate, Bisphenol A diallyl etherand the diadduct of toluene diisocyanate and diallyl malate.

The polythiol component has a molecular weight in the range from about50 to about 20,000 and the general formula:

R 4-SH),

wherein R, represents a polyvalent organic moiety free from reactivecarbon-to-carbon unsaturation and B is a numeral of at least 2. Thus, Rmay contain cyclic groupings and hetero atoms such as N, P, or O andprimarily contains carbon-carbon, carbon-hydrogen, carbon-oxygen orsilicon-oxygen containing chain linkages free of any reactivecarbon-to-carbon unsaturation. The ene/thiol mole ratio is selected soas to provide a solid, self-supporting cured product under ambientconditions in the presence of a free radical generator.

The polythiol may be a simple or complex organic compound having amultiplicity of pendant or terminally positioned SH functional groupsper average molecule.

On the average, the polythiol must contain 2 or more SH groups/moleculeand have a viscosity range of essentially 0 to 20 million centipoises(cps) at C as measured by a Brookfield Viscometer either alone or whenin the presence of an inert solvent, aqueous dispersion or plasticizer.Operable polythiols usually have molecular weights in the range about toabout 20,000, and preferably from about 200 to about 10,000.

One class of polythiols curable with polyenes to obtain essentiallyodorless polythioether products are esters of thiol-containing acids ofthe formula HSR- COOH where R is an organic moiety containing noreactive carbon-to-carbon unsaturation with polyhydroxy compounds ofstructure R t-H),, where R is an organic moiety containing no reactivecarbon-tocarbon unsaturation, and n is 2 or greater. These componentswill react under suitable conditions to give a polythiol having thegeneral structure:

ll R;-O c-m-srr where R and R are organic moieties containing noreactive carbon-to-carbon unsaturation, and n is 2 or greater.

Certain polythiols such as the aliphatic monomeric polythiolsexemplified by ethane dithiol, hexamethylene dithio, decamethylenedithiol, tolylene-2,4-dithiol, and the like, and some polymericpolythiols such as a thiolterminated ethylcyclohexyl dimercaptanpolymer, and the like, and similar polythiols which are conveniently andordinarily synthesized on a commercial basis, although having obnoxiousodors, are operable but many of the end products may not be widelyaccepted from a practical, commercial point of view.

The preferred polythiol compounds are characterized by a low level ofmercaptan-like odor initially, and after reaction, give essentiallyodorless polythioether coatings which are commercially attractive andpractically useful for both indoor and outdoor applications.

Examples of the polythiol compounds preferred because of relatively lowodor level include but are not limited to esters of thioglycolic acid(HS-CH- -COOH), Z-mercaptopropionic acid (HSCH(CH- )COOl-l) and3-mercaptopropionic acid (HS-Cl-hCl-QCOOH) with polyhydroxy compoundssuch as glycols, triols, tetraols, pentaols, hexaols, and the like.Specific examples of the preferred polythiols include but are notlimited to ethylene glycol bis (thioglycolate), ethylene glycol bis(3-mercaptopropionate), trimethylolpropane tris (thioglycolate),trimethylolpropane tris (3-mercaptopropionate), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis (B-mercaptopropionate), andpentaerythritol tetrakis (3-mercaptopropyl ether), all of which arecommercially available. A specific example ofa preferred polymericpolythiol is polypropylene ether glycol bis (3-mercaptopropionate) whichis prepared from polypropylene-ether glycol (e.g., Pluracol P2010,Wyandotte Chemical Corp.) and 3-mercaptopropionic acid byesterification.

Resins useful herein include linear or branched polyesters, preferablylinear, having molecular weight from about 500 to about 100,000 andpreferably from about 1,000 to about 50,000 which may be prepared byreacting a polybasic acid or anhydride having the general formula 0 [RJ(b-on) in acid form with a polyhydric alcohol having the general formula[R ]-4-Ol-l),, wherein x and y are numerals of 2 or more and preferably2 to 4, and R and R are saturated or unsaturated hydrocarbyl groupshaving valence ofx and y respectively.

The polybasic acid or anhydride reactant may be, for example, phthalicacid or phthalic anhydride, maleic acid or maleic anhydride, adipicacid, trimellitic acid or trimellitic anhydride, succinic acid orsuccinic anhydride, fumaric acid, terephthalic acid, itaconic acid,glutaric acid, isophthalic acid, the adduct of levopimaric acid withmaleic acid, and mixtures thereof.

The polyhydric alcohol reactant may be, for example, ethylene glycol,diethylene glycol, polyethylene glycol, propylene glycol, dipropyleneglycol, polypropylene glycol, l,3-propanediol, 1,4-butanediol, neopentylglycol, penaerythritol, glycerol, trimethylolpropane, Bisphenol A(4,4'-isopropylidenediphenol), and l,4-dihydroxymethylbenzene.

Other soluble resins which are useful herein are polyester-polyeneswhich may be prepared by capping the polyester resins describedhereinabove with a member having the general formula wherein R typicallyrepresents a saturated alkyl member having a molecular weight from aboutl00 to about 400, p and q are numerals from 0 to 10 and preferably 1with the sum of p and q always equal to or greater than 1, and with rbeing a numeral from 1 to 10 and preferably from 2 to 8. Alternatively,[R may be ab sent, in which instance the hydroxyl and/or carboxyl groupsare joined directly to [R as exemplified by allyl alcohol or acrylicacid. Typically, the sums of numerals x and p are approximately equal tothe sums of numerals y and r.

In the above formula, [R-,] may be selected from the group consistingof:

In the groups (a) to (e),fis an integer from 1 to 9; R is a radicalselected from the group consisting of hydrogen, fluorine, chlorine,furyl, thienyl, pyridyl, phenyl and substituted phenyl, benzyl andsubstituted benzyl, alkyl and substituted alkyl, alkoxy and substitutedalkoxy, and cycloalkyl and substituted cycloalkyl. The substituents onthe substituted members are selected from the group consisting of nitro,chloro, fluoro, acetoxy, acetamide, phenyl, benzyl, alkyl, alkoxy andcycloalkyl. Alkyl and alkoxy have from i to 9 carbon atoms andcycloalkyl has from 3 to 8 carbon atoms.

Useful capping agents include, for example, allyl alcohol,trimethylolpropane diallyl ether, diallyl malate, diallyl tartrate,2-vinyloxyethanol, vinyl hydroxyethyl sulfide, IO-undecylenyl alcohol,allyl maleate, allyl phthalate, diallyl trimellitate, N-Methyl-N-vinylethanolamine, and 4-vinyloxybenzyl alcohol.

The polyester-polyene resin has a molecular weight in the range fromabout 64 to 20,000, preferably about 200 to about 10,000 and a viscosityin the range from essentially 0 to 20 million centipoises at 70C. asmeasured by a Brookfield viscometer. The polyesterpolyene ischaracterized by having at least two unsaturated carbon-to-carbon bondsdisposed at terminal or near terminal positions on a main chain of themolecule or pendent therefrom.

It is found that the polyester-polyene resin is cocurable, i.e., uponexposing the lacquer to a free radical generator such as actinicradiation the polyesterpolyene reacts with a portion of the polythiol ina manner generally analogous to the polyene component to formpolythioether linkages. Advantageously, however, the polyester-polyenesgenerally minimize the amount of polythiol necessary to effect curing ofthe lacquer composition to solid durable overcoatings.

The polyester-polyenes are disclosed in copending Guthrie application,Curable Liquid Pigment Composition and Method," Ser. No. 188,608, filedOct. 12, 197 l, assigned to the same assignee hereof and incorporatedherein in pertinent part by reference.

Other resins which may be included in the present lacquer compositioninclude, for example, carbohydrates, preferably sucrose octa-acetate andsucrose acetate-butyrate. Still other resins useful herein include, forexample, polyvinyl acetate, polyvinyl alcohol, polystyrene, esters ofabietic acid, polymers of aor B-pinene, indenecoumarone copolymers, andthe like.

Other resins which may usefully be included in the lacquer compositionare liquid plasticizers such as polyethylene glycol having molecularweight of up to about 400, dioctyl phosphate, dibutyl phthalate and thelike.

The resin component may be included in any effective amount. Generally,the resin may suitably be included in an amount from about 1 to about 50parts by weight, and preferably from about 10 to about 50 parts byweight, per 100 parts by weight of polyene-polythiol combination.

The polyene has two or more reactive unsaturated carbon-to-carbon bondslocated terminal from the main chain. The polythiol has two or morethiol groups per molecule. After the polyene, polythiol and resin arecombined and if desired, with additional materials, as may be required,the curable lacquer composition is applied to a printed substrate andthereafter exposed to a free radical generator such as actinic radiationto give an essentially odorless solid elastomeric overcoating. Althoughas a practical matter, actinic radiation is preferred, it is recognizedthat chemical free radical generating reagents may be employed as wellas high energy radiation bombardment.

Although the mechanism of the curing reaction is not completelyunderstood, it appears most likely that the curing reaction may beinitiated by most any chemical free radical generating reagent whichdissociates or abstracts a hydrogen atom from an SH group, oraccomplishes the equivalent thereof.

Generally the rate of the curing reaction may be increased by increasingthe temperature of the composition at the time of initiation of cure. Inmanyapplications, however, the curing is accomplished conveniently andeconomically by operating at ordinary room temperature conditions.

The present curable lacquer compositions are characterized byinsensitivity to visible light, rendering them generally free fromsetting on, for example, apparatus which may be used to apply thecomposition to a substrate. Upon exposure to actinic light, the presentlacquer compositions are found to be rapidly curable making thememinently suitable for use in high speed coating operations.

A class of actinic light useful herein for curing is ultraviolet lightand other forms of actinic radiation which are normally found inradiation emitted from the sun or from artificial sources such as typeRS sunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps,tungsten halide lamps and the like. Ultraviolet radiation may be usedmost efficiently if the curable lacquer composition contains a suitablephotocuring rate accelerator.

Curing periods may be adjusted to be very short and hence commerciallyeconomical by proper choice of ultraviolet source, photocuring rateaccelerator and concentration thereof, temperature and molecular weight,and reactive group functionality of the polyene and polythiol. Curingperiods of less than about 1 second duration are possible in preparinglacquer coatings having thickness in the range from about 0.1 to about0.5 mil and even to about 2 mils in some applications.

Conventional curing inhibitors or retarders which may be used in orderto stabilize the components of the curable lacquer compositions so as toprevent premature onset of curing may include hydroquinone; p-tert.-butyl catechol; 2,6-ditert.-butyl-p-methylphenol; phenothiazine;N-phenyl-2-naphthylamine; inert gas atmo spheres such as helium, argon,nitrogen and carbon dioxide; vacuum; and the like. Acidic stabilizerssuch as phosphorous acid and the like may be usefully employed.

It is further understood that the polyene and the polythiol may beformed in situ in the photocurable lacquer composition without departingfrom the spirit of this invention.

Specifically useful herein are chemical photocuring rate acceleratorssuch as benzophenone, acetophenone, azobenzone, acenapthene-quinone,o-methoxy benzophenone, Thioxanthen-Q-one, xanthen-9-one, 7- H-Benz [de]anthracen-7-one, dibenzosuberone, lnaphththaldehyde, 4,4-bis(dimethylamino) benzophenone, fluorene-9-one, l'-acetonaphthone, 2-acetonaphthone, anthraquinone, l-indanone, 2-tert.- butyl anthraquinone,valerophenone, hexanophenone, 8-phenyl-butyrophenone,p-morpholinopropiophenone, 4-morpholino-benzophenone, 4'-morpholinodeoxybenzoin, p-diacetylbenzene, 4- aminobenzophenone,4'-methoxyacetophenone, benzaldehyde, a-tetralone, 9-acetylphenanthrene,2- acetylphenanthrene, IO-thioxanthenone 3- acetylphenanthrene,3-acetylindole, 1,3,5-triacetylbenzene and the like, including blendsthereof to greatly reduce the exposure times.

The curing rate accelerators are'usually added in an amount ranging fromabout 0.0005 to about 50 percent by weight of the photocurable lacquercomposition, with a preferred range being from about 0.05 to about 25percent by weight. Preferred photocuring rate accelerators are thealdehyde and ketone carbonyl com pounds having at least one aromaticnucleus attached directly to the group.

The relative amounts of polyene and polythiol in cluded in thephotocurable lacquer composition are selected such that the mole ratioof enezthiol is from about 0.221 to about :1, and preferably from about0.75:1 to about 1.5:1.

Practice of the present invention will be further illustrated by thefollowing non-limiting examples wherein all parts and percentages givenare by weight unless indicated otherwise.

EXAMPLE 1 275 grams (1.86 moles) of phthalic anhydride, 60.8 grams (0.62mole) of maleic anhydride, 90.5 grams (0.62 mole) of adipic acid, and328 grams (3.09 moles) of diethylene glycol were heated in a vessel for3 hours at 200C. The resulting polyester resin product was cooled andremoved from the vessel. A photocurable lacquer composition was preparedby mixing at 50C grams of the resin (a solid at 25C) with 10 grams (0.04mole) of triallyl isocyanurate, 14 grams (0.03

mole) of pentaerythritol tetrakis (3-mercaptopropionate), 0.5 gram ofbenzophenone, 0.025 gram of phosphorous acid, and 0.05 gram of lrganox1076 (trademark for a hindered phenol antioxidant product by GeigyIndustrial Chemicals). The mixture was heated to 70C to dissolve thebenzophenone producing a clear homogeneous mixture having a viscosity inthe range of 12,000 to 18,000 cps and a pH in the range of 4.5 to 5.5.

The photocurable lacquer was applied at 25C to steel can body stockhaving a red printing ink printed thereon by conventional techniques.The lacquer was applied as a liquid film having a thickness of 0.2 to0.4 mil using a conventional roller coater. The area of applicationincluded the printed area plus adjacent nonprinted portions of thesteel. The applied liquid film was exposed to ultraviolet light using a5000 watt Hanovia lamp positioned 4 inches from the film. Exposure wasfor 3 to 5 seconds, during which time the liquid film cured to a clearsolid coating which was found to be characterized with high gloss,strong bonding to both the printed ink and the steel, and excellentabrasion resistance.

EXAMPLE 2 A polyester resin was prepared at 200C. using the resinpreparation procedure of Example 1 except that, prior to cooling, 4.3grams (0.02 mole) of trimethylolpropane diallyl ether was added and thetemperature of the reactants was increased to 240C, which temperaturewas maintained for l hour. The resin product was cooled and removed fromthe vessel. Analysis of the product showed it to be apolyester-tetraene'which was a solid at 25C. A curable lacquercomposition was prepared by mixing 10 grams of this polyester-tetraeneat 60C with 10 grams (0.04 mole) of triallyl isocyanurate, 14 grams(0.03 mole) of pentaerythritol tetrakis (3-mercaptopropionate), 0.5 gramof benzophenone, 0.025 gram of phosphorous acid and 0.05 gram of Irganox1076. This lacquer composition was applied asa film on printed steel canbody stock and thereafter cured using the application and curingprocedures of Example 1. The cured lacquer coating was found to becharacterized with good clarity, high gloss, strong .bonding to theprinted ink and the steel, and excellent abrasion resistance.

EXAMPLE 3 12 grams of commercially available polyethylene glycol havinga molecular weight of 400 was mixed with 10 grams of triallylisocyanurate, 14 grams of pentaerythritol tetrakis(3-mercaptopropionate), 0.5 gram of benzophenone, 0.025 gram ofphosphorous acid, and 0.05 gram of Trganox 1076. The resultingphotocurable lacquer composition was roller-coated at 20to 30C ontopaperboard having ink printed thereon. The area of lacquer applicationincluded printed and non printed areas. The coated paperboard wasexposed to ultraviolet light using a 5000 watt Hanovia lamp positioned 3inches from the paperboard. Exposure was for 3 to 5 seconds, duringwhich time the lacquer cured to a clear solid coating which was found tobe characterized with high gloss, strong bonding to both the printed inkand the paper-board and excellent abrasion resistance.

EXAMPLE 4 10 grams of liquid polyester resin LB 104-45 (commerciallyavailable from Marco Chemical Division of W. R. Grace & Co.) was mixedwith 10 grams of allyl isocyanate, 14 grams of pentaerythritol tetrakis(3-mercaptopropionate), 0.5 gram of benzophenone, 0.025 gram ofphosphorous acid, and 0.05 gram of Irganox lO76. A thin film of theresulting photocurable lacquer composition was applied to ink-printedand non-printed areas of steel can body stock using a roller. Next, thefilm was cured using the curing procedure of Example 1. The curedlacquer coating was found to be characterized with good clarity, highgloss, strong bonding to the printed ink and the steel, and excellentabrasion resistance.

EXAMPLE 5 A curable lacquer composition was prepared by mixing at 55C 10grams of the polyester-tetraene resin of Example 2 with 10 grams (0.04mole) of triallyl isocyanurate, 10 grams of Bisphenol A diallyl ether,23 grams of pentaerythritol tetrakis (3-mercaptopropionate), 0.5 gram ofdibenzosuberone and 0.05 gram of Irganox 1076. This lacquer compositionwas applied as a 3-mil film on printed steel can body stock andthereafter cured using the application and curing procedures ofExample 1. The cured lacquer coating was found to be characterized withgood clarity, high gloss, strong bonding to the printed ink and steeland excellent abrasion resistance.

EXAMPLE 6 A photocurable lacquer was prepared at 65C by mixing 10 gramsof the polyester-tetraene resin of Example 2 with 31 grams of BisphenolA diallyl ether, 24 grams of pentaerythritol tetrakis(3-mercaptopropionate), 1 gram of benzophenone and 0.05 gram of Irganox1076. This photocurable lacquer was applied at 25-30C to steel can bodystock having ink printed thereon. The lacquer was applied as a liquidfilm with a thickness of 0.3 to 0.5 mil using a conventional rollercoater. The area of application included the printed area plus adjacentnon-printed portions of the steel. The applied liquid film was exposedto ultraviolet light, using a 4000 watt Ferro lamp positioned 3 to 4inches from the film. Exposure was for 3-5 seconds, during which timethe liquid film cured to a clear solid coating which was found to becharacterized with high gloss, strong bonding to both the printed inkand the steel, and excellent abrasion resistance.

EXAMPLE 7 A photocurable lacquer was prepared at 60C by mixing 10 gramsof the polyester-tetraene resin of Example 2 with 31 grams of BisphenolA diallyl ether, 24 grams of pentaerythritol tetrakis (3-mercaptopropylether), 2 grams of benzophenone, and 0.05 gram of Irganox 1076. A thinfilm of this photocurable lacquer composition was applied at C tomagazine quality paper having ink printed thereon. The lacquer wasapplied as a liquid film having a thickness of 0.05 to 0.1 mil using aconventional roller coater. The area of application included the printedarea plus non-printed portions of the paper. The applied liquid film wasexposed to ultraviolet light using a 5000 watt Hanovia lamp positioned 4inches from the film. Exposure was for about 3 seconds, during whichtime the liquid film cured to a clear solid coating which was found tobe characterized with high gloss, strong bonding to both the printed inkand the paper, and excellent abrasion resistance.

EXAMPLE 8 459 grams (3.1 moles) of phthalic anhydride and 296 grams(3.09 moles) of ethylene glycol were heated in a vessel for 4 hours at190C. Next, 4.28 grams (0.02 mole) of trimethylolpropane diallyl etherwas added. The temperature of the reactants was increased to 230C, whichtemperature was maintained for 1 hour. The resin product was cooled andremoved from the vessel. Analysis of the product showed it to be apolyester-tetraene which was a solid at 25C. A curable lacquercomposition was prepared by mixing 12 grams of this polyester-tetraeneat 50C. with 10 grams of triallyl isocyanurate 14 grams ofpentaerythritol tetrakis (3-mercaptopropionate), 0.5 gram ofbenzophenone, 0.025 gram of phosphorous acid, and 0.05 gram of Irganox1076. This lacquer composition was applied as a thin film at 25to C onprinted steel can body stock and thereafter cured using the applicationand curing procedures of Example 1. The cured lacquer coating was foundto be characterized with good clarity, high gloss, strong bonding to theprinted ink and the steel and excellent abrasion resistance.

EXAMPLE 9 To a resin kettle maintained under a nitrogen atmosphere andequipped with a condenser, stirrer, thermometer and gas inlet and outletwas added 174 grams 1 mole) of toluene diisocyanate, 428 grams (2 moles)of diallyl malate, along with 0.3 gram of stannous octoate as catalyst,and the reaction was continued for 2 hours at 60C. 20 grams of the thusformed tetraene diadduct of diallyl malate and toluene diisocyanate wasEXAMPLE 10 The procedure of Example 9 was repeated except that 528 grams(2 moles) of 3,3'-dimethyl-4,4- biphenylene diisocyanate was substitutedfor the toluene diisocyanate. The results were substantially the same.

EXAMPLE 1 l The procedure of Example 9 was repeated except that 358grams (2 moles) of 3-isocyanatomethyl-3,5,5- trimethylcyclohexylisocyanate was substituted for the toluene diisocyanate. The resultswere substantially the same.

EXAMPLE 12 The procedure of Example 9 was repeated except that 500 grams(2 moles) of 4,4-

methylenebis(cyclohexyl isocyanate) was substituted for the toluenediisocyanate. The results were substantially the same.

EXAMPLE 13 The procedure of Example 9 was repeated except that 116 grams(2 moles) of allyl alcohol was substituted for the diallyl malate. Theresults were substantially the same.

EXAMPLE 14 The procedure of Example 9 was repeated except that 430 grams(2 moles) of trimethylol propane diallyl ether was substituted for thediallyl malate. The results were substantially the same.

EXAMPLE 15 343 grams (1.1 mole) of 4,4'-diglycidyl ether of Bisphenol A(commercially available under the name Epon 828 by Shell Chemical Co.)was charged to a dry resin kettle maintained under nitrogen and equippedwith a condenser, stirrer, thermometer and gas inlet and outlet. 190grams (2 moles) of diallyl amine was added to the kettle and thereaction was continued with stirring for 3 hours at C. A photocurablelacquer composition was prepared at 55C by mixing 12.6 grams of the thusformed tetraene diadduct with 122 grams of pentaerythritol tetrakis(3-mercaptopropionate), 10 grams of the polyester-tetraene resin ofExample 2, 1 gram of dibenzosuberone and 0.05 gram of Irganox 1076. Afilm of this photocurable lacquer composition was applied to printedsteel can body stock and thereafter cured using the coating and curingprocedures of Example 1. The results were substantially the same.-

EXAMPLE 16 To a resin kettle maintained under a nitrogen atmosphere andequipped with a condenser, stirrer, thermometer and a gas inlet andoutlet was added 179 grams 1 mole) of3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate. 116 grams (2moles) of allyl alcohol was added and the reaction was continued for 4hours at 90C with stirring. 100 grams of the resulting diene diadduct ofallyl alcohol with the 3- isocyanatomethyl-3,5,S-trimethylcyclohexylisocyanate was mixed with 83.5 grams of pentaerythritol tet rakis(3-mercaptopropyl ether), 40 grams of the polyester-tetraene resinprepared in Example 8, 2 grams of dibenzosuberone, and 0.2 gram oflrganox 1076. This photocurable lacquer composition was applied as afilm and thereafter cured on steel can body stock having ink printedthereon using the application and curing procedures of Example 1. Theresults were substantially the same.

EXAMPLE 17 4.3 grams (0.2 mole) of trimethylolpropane diallyl ether wasadded to a resin kettle maintained under a nitrogen atmosphere having acondenser, stirrer, thermometer, and gas outlet and inlet. Next, 264grams (1 mole) of 3,3dimethyl-4,4'-phenylene diisocyanate and 0.5 gramof dibutyl tin dilaurate catalyst were added. Reaction was continued for5 hours at 120C with stirring. 20 grams of the resulting tetraenediadduct was mixed with 16 grams of pentaerythritol tetrakis(3-mercaptopropionate grams of the polyestertetraene resin of Example 2,1 gram of dibenzosuberone and 0.1 gram of lrganox 1076. A cured coatingof this photocurable lacquer composition was formed on printed steel canbody stock using the application and curing procedures of Example l. Theresults were substantially the same.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that numerous variations can be madetherein without departing from the spirit or scope of the presentinvention.

What is claimed is:

l. A photocurable lacquer composition comprising (A) a polythiolcomponent containing at least 2 SH groups per molecule (B) the adduct of2 moles of diallyl malate per mole of toluene diisocyanate as polyene;the relative amounts of polyene to polythiol being selected such thatthe mole ratio of ene to thiol is from about 0.2:1 to about 5:1; (C)from about 0.0005 to about 50 percent by weight of the composition of aphotocuring rate accelerator component; (D) from about 1 to about 50parts by weight per parts by weight of the polyene-polythiol combinationof a polyester-polyene prepared by reacting (a) phthalic anhydride and(b) ethylene glycol to form a polyester resin and capping said polyesterresin with (c) trimethylolpropane diallyl ether, the mole ratio of(a):(b): (c) being about 3.123.110.02.

2. The composition of claim 1 wherein the polythiol has a molecularweight in the range from about 100 to about 20,000.

3. The composition of claim 1 wherein the polyester has a molecularweight in the range from about 500 to about 100,000.

4. A method for overcoating which comprises applying to a substrate thelacquer composition of claim 1, and thereafter exposing the appliedcomposition to ultra violet radiation in the wave length range from 100to 3,800 Angstroms for a period of time sufficient to photocure thecomposition.

5. A method for overcoating which comprises applying to a substrate thelacquer composition of claim 2, and thereafter exposing the appliedcomposition to ultra violet radiation in the wave length range from 100to 3,800 Angstroms for a period of time sufficient to photocure thecomposition.

6. A method for overcoating which comprises applying to a substrate thelacquer composition of claim 3, and thereafter exposing the appliedcomposition to ultra violet radiation in the wave length range from 100to 3,800 Angstroms for a period of time sufficient to photocure thecomposition.

7. The method of claim 4 wherein the applied composition is from about0.1 to about 2 mils in thickness.

8. The method of claim 4 wherein the lacquer composition is applied to aprinted substrate.

1. A PHOTOCURABLE LACQUER COMPOSITION COMPRISING (A) A POLYTHIOCOMPONENT CONTAINING AT LEAST 2 - SH GROUPS PER MOLECULE (B) THE ADDUCTOF 2 MOLES OF DIALLY MALATE PER MOLE OF TOLUENE DIISOCYANATE AS POLYENE;THE RELATIVE AMOUNTS OF POLYENE TO POLYTHIOL BEING SELECTED SUCH THATTHE MOLE RATIO OF ENE TO THIOL IS FROM ABOUT 0.2:1 TO ABOUT 5:1; (C)FROM ABOUT 0.005 TO ABOUT 50 PERCENT BY WEIGHT OF THE COMPOSITION OF APHOTOCURING RATE ACCELERATOR COMPONENT; (D) FROM ABOUT 1 TO ABOUT 50PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF THE POLYENE-POLYTHIOLCOMBINATION OF A POLYESTER-POLYENE PREPARED BY REACTING (A) PHTHALICANHYDRIDE AND (B) ETHYLENE GLYCOL TO FORM A POLYESTER RESIN AND CAPPINGSAID POLYESTER RESIN WITH (C) TRIMETHYLOLPROPANE DIALLYL ETHER, THE MOLERATIO OF (A): (B): (C) BEING ABOUT 3.1:3.1:0.02.
 2. The composition ofclaim 1 wherein the polythiol has a molecular weight in the range fromabout 100 to about 20,000.
 3. The composition of claim 1 wherein thepolyester has a molecular weight in the range from about 500 to about100,000.
 4. A method for overcoating which comprises applying to asubstrate the lacquer composition of claim 1, and thereafter exposingthe applied composition to ultra violet radiation in the wave lengthrange from 100 to 3,800 Angstroms for a period of time sufficient tophotocure the composition.
 5. A method for overcoating which comprisesapplying to a substrate the lacquer composition of claim 2, andthereafter exposing the applied composition to ultra violet radiation inthe wave length range from 100 to 3,800 Angstroms for a period of timesufficient to photocure the composition.
 6. A method for overcoatingwhich comprises applying to a substrate the lacquer composition of claim3, and thereafter exposing the applied composition to ultra violetradiation in the wave length range from 100 to 3,800 Angstroms for aperiod of time sufficient to photocure the composition.
 7. The method ofclaim 4 wherein the applied composition is from about 0.1 to about 2mils in thickness.
 8. The method of claim 4 wherein the lacquercomposition is applied to a printed substrate.